The invention relates to the pressure swing adsorption process (PSA) for the separation of a gaseous mixture.
In general, in the PSA process, the first phase comprises selectively adsorbing components of the feed gas under pressure to obtain a gaseous stream depleted of the adsorbable components. Following the adsorption phase, the adsorber is subjected to multistage expansion to desorb the previously adsorbed components. Then the pressure is increased to the adsorption pressure and the cycle is repeated. By this operating sequence, there is obtained a residual gas consisting of desorbed components and purge gas in addition to the product gas consisting essentially of unadsorbed components.
It has also been suggested to obtain, besides the unadsorbed products, also the adsorbed components in as pure a form as possible. In this method, described in DOS No. 2,604,305, this reference being incorporated herein, an adsorber loaded with adsorbable components is first further saturated with adsorbable component in order to displace unadsorbable gas that has remained in the interstitial voids of the adsorber. Thereafter, the pressure in the adsorber is lowered, preferably to subatmospheric pressure, to obtain a stream of desorbate as the secondary product. In order to avoid contamination of this secondary product, no purge gas is employed in this process.